All Bitcoin private keys is simply an integer between number 1 and 115792089237316195423570985008687907852837564279074904382605163141518161494337 or HEX: from 1 to 0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141. The integer range of valid private keys is governed by the secp256k1 ECDSA standard used by Bitcoin.

In order to make copying of private keys less prone to error, Wallet Import Format may be utilized. WIF uses base58Check encoding on a private key, greatly decreasing the chance of copying error, much like standard Bitcoin addresses.

Take a private key.

Add a 0x80 byte in front of it for mainnet addresses.

Append a 0x01 byte after it if it should be used with compressed public keys. Nothing is appended if it is used with uncompressed public keys.

Perform a SHA-256 hash on the extended key.

Perform a SHA-256 hash on result of SHA-256 hash.

Take the first four bytes of the second SHA-256 hash; this is the checksum.

Add the four checksum bytes from point 5 at the end of the extended key from point 2.

The process is easily reversible, using the Base58 decoding function, and removing the padding.

Bitcoin compressed address.

A compressed address is just the way of storing a public key in fewer bytes (33 instead of 65). There are no compatibility or security issues because they are precisely the same keys, just stored in a different way. The original Bitcoin software didn't use compressed keys only because their use was no disadvantages other than that a little bit of additional computation is needed to validate a signature.

Get Lucky page.

You will see 20 random generated private keys, addresses, quantity of transactions and current balance to each Bitcoin address.

What is your chance to get luck ?
Divide 115,792,089,237,316,195,423,570,985,008,687,907,852,837,564,279,074,904,382,605,163,141,518,161,494,337 into 20
Yes, it's a rare chance tending to zero. Nobody is supposed to get these Bitcoins.

Can Google crowl all pages and compromise private keys ?

Theoretically, some private keys and Bitcoins addresses can be vulnerable, because Google search engine (Bing, Yandex etc...) can index some pages with private keys and addresses. But indexing all the pages is a huge array of keys.

For example: one of our pages with 100 addresses is about 40 978 Bytes. Try to divide the number of all the addresses into 100 (rows per page), multiply by 40 978 Bytes and divide into 137438953472 (one TerraByte).

You will get 345,238,967,039,530,911,720,582,795,073,715,758,043,805,378,040,119,207,565,323,040,414,160 TeraBytes of pages (!)